Heretofore, it has been known to utilize permanent magnet rotor assemblies in conjunction with wound stator assemblies to produce compact motor units. Typically, segmented magnets are mounted within a cup-like containment fixture to form a rotor assembly. A wound stator assembly is located inside the rotor to provide the electromagnetic force needed to rotate the rotor assembly relative to the stator. A primary drawback associated with such known motor assemblies is the lack of support provided by the cups typically used. Conventional thin gauge cups, while being inexpensive, lightweight and capable of high speed rotation, do not provide the rotational stiffness or rigidity needed to support the conventional magnets. As such, flexing of the cup at high rotational speeds results in breakage of the magnets. Attempts at eliminating breakage have focused on basically three types of solutions to this problem. The first and most obvious solution is to run the motor at lower rotational speeds to reduce flexing of the cup and in-turn magnet breakage. This solution is unsatisfactory in many applications particularly where high speed capabilities are desired or required. The second attempted solution has been to utilize magnets having a high degree of inherent mechanical strength so as to resist breakage even when the cup flexes. This solution is similarly unsatisfactory as such magnets tend to be more expensive and heavier than conventional magnets. The extra weight of such magnets not only adds to the overall weight of the motor but also significantly increases assembly inertia at high speeds. Such an increase in inertia is undesirable in many applications. The third solution has been to manufacture cups from either heavier gauge material or alternative materials having a higher degree of rotational stability. This solution, likewise is unsatisfactory as it results in increased weight, increased material cost and increased manufacturing costs, all of which are undesirable.
Accordingly, there is a desire, as well as a need, to obtain a motor assembly which uses conventional magnets and thin gauge cup material while providing sufficient rotational rigidity to eliminate magnet breakage at high rotational speeds, without a significant increase in assembly inertia.